Field of the Invention
The present invention provides methods of manufacturing a cylindrical tubular substrate for an electrophotographic photoconductor. In particular, the present invention is directed to a method of injection molding of a plastic material for the manufacture of multiple types of electrophotographic photoconductor substrates having various lengths.
Photoconductors are used in electrophotographic apparatuses such as copy machines and printers that utilize electrophotographic techniques. Photoconductors comprise a conductive substrate and a photoconductive layer laminated on the conductive substrate. The conductive substrate is generally formed as a cylindrical tube having a peripheral layer onto which the photoconductive layer is laminated.
Aluminum and aluminum alloys have been widely used in the manufacture of the cylindrical substrates due to their light weight and excellent machinability. However, very precise machining of the peripheral surface of each cylindrical aluminum or aluminum alloy substrate is required to achieve the exact required dimensional precision and preferred surface roughness. Precise machining of both ends of the substrate is required so that a flange for rotating the substrate can be fitted at one end, and a flange for fixing the rotating shaft can be fitted at the other end of the substrate. External surface contaminations must be washed from the substrate before forming the photoconductive layer. Since the aluminum or aluminum alloy surface is sensitive to the storage environment, it is necessary to adopt countermeasures against surface alteration, such as covering the substrate surface with an oxide film. Accordingly, multiple steps and high costs are associated with the manufacture of aluminum and aluminum alloy substrates.
Japanese Examined Patent Publication No. HO2-17026 (JP 90017026) discloses a cylindrical substrate that is lighter in weight than an aluminum or aluminum alloy substrate, highly chemically and thermally resistant, neither oxidized nor deformed by air, and compatible with photoconductors. The cylindrical substrate is manufactured by injection molding of a material containing a polyphenylene sulfide (PPS) resin.
Manufacture of aluminum or aluminum alloy substrates of different lengths is accomplished by manufacturing a long cylindrical tubing, for example by drawing, cutting the tubing at every desired length, and forming spigot joints for inserting flanges on both open ends of the cut tube. In contrast, substrates of the plastic material may be formed together with the spigot joints by injection molding with a molding die of the desired shape and dimension. The shape and dimension of each cylindrical substrate are thus defined by the particular molding die used in injection molding. Accordingly, multiple molding dies are necessary to manufacture cylindrical substrates of different lengths.
Another disadvantage of the prior art methods of manufacturing cylindrical substrates results from the slanted inner surfaces of the substrate tubes. The core die, a part of an injection molding die, has a slanted surface to allow the molded substrate to be easily removed from the molding die. The slanted surface of the core die causes slanting of the inner surface of the cylindrical substrate tube with respect to its axis of rotation. Due to the slanted inner surface of the cylindrical substrate, flanges fixed on the open ends of the substrate tubes tend to slip out of the substrate tubes.
Accordingly, there is a need in the art for better methods of manufacturing photoconductor substrates. The present invention solves the problems of the prior art methods by providing a method for manufacturing multiple plastic photoconductor substrates by using a single molding die. The photoconductor substrates made by the present method have differing lengths, and open ends to which flanges can be secured tightly.